1. Field of the Invention
The present invention relates to a pump of an electronically controlled brake system, and, more particularly, to a pump of an electronically controlled brake system in which an outlet valve has a simplified configuration, thereby achieving a reduction in manufacturing costs.
2. Description of the Related Art
In general, an electronically controlled brake system has the purpose of efficiently preventing a wheel slip caused upon braking, quick start, or sudden acceleration of a vehicle. The brake system includes a plurality of solenoid valves to control a braking hydraulic pressure to be transmitted to hydraulic brakes of vehicle wheels, a pair of low-pressure and high-pressure accumulators to temporarily store an oil discharged from the hydraulic brakes, a pair of pumps provided between the low-pressure and high-pressure accumulators, the pumps being operated by a motor, and an ECU to control operations of the solenoid valves and motor. All the above elements are received in a modulator block made of aluminum.
In a vehicle having the above-described electronically controlled brake system, a braking force is selectively applied to a front axle or rear axle to regulate the hydraulic pressure to be transmitted to the wheel brakes, resulting in traveling stability of the vehicle. In this case, the pair of pumps serves to forcibly pump the low-pressure oil stored in the low-pressure accumulator to the high-pressure accumulator, so as to transfer the oil to the hydraulic brakes or master cylinder.
FIG. 1 is a sectional view showing a conventional pump of an electronically controlled brake system.
As shown in FIG. 1, the pump, which is designated by reference numeral 10, is installed in a block 1 that incorporates an oil passage and a variety of valves. An eccentric motor 2 is installed in the center of the block 1 and generates an eccentric rotating force. A bore 3 for installation of elements of the pump 10 is also formed in the block 1.
A piston 11 is installed in the bore 3, to perform rectilinear reciprocation using the eccentric force supplied from the eccentric motor 2.
The piston 11 has one end in contact with an outer circumference of an eccentric bearing (not designated by a reference numeral) of the eccentric motor 2, and the other end of the piston 11 is provided with a ball-shaped inlet valve 12.
An O-ring 13, as a seal, is fitted on an outer circumference of the piston 11. Also, an inlet path 14 for introduction of oil from a low-pressure accumulator is defined at the outer circumference of the piston 11.
The piston 11 has a hollow inner space 15, and a duct 16 is formed in the piston 11 to connect the hollow inner space 15 and the inlet path 14 with each other.
Here, the inlet valve 12 and piston 11 are elastically supported by a supporting spring 17, an entrance-side spring 18, and a return spring 19.
An outlet valve is provided at an end of the return spring 19 opposite to the inlet valve 12. The outlet valve includes an exit-side valve seat 21, a pump plug 22 caulked to the exit-side valve seat 21, and a ball-shaped closing member 24 supported in the pump plug 22 by means of an exit-side spring 23.
However, in the above-described conventional pump of an electronically controlled brake system, due to a complicated configuration of the outlet valve, in particular, of the valve seat 21, pump plug 22, etc., there is a problematic increase in manufacturing costs required for processing and assembly of the above elements.
Further, the conventional pump suffers from operation noise caused by pulsation of fluid that flows through an outlet path according to opening/closing operations of the outlet valve. The fluid pulsation also results in abnormal tactile feedback from a brake pedal.